A lawyer for Sambi said he was being held in “prison-like” conditions.
The ex-president, who was in power from 2006 to 2011, has previously denied all allegations against him.
Comoros launched a programme with the United Arab Emirates and Kuwait in 2008 to sell citizenship to stateless people in those countries in return for cash to help develop the poor Indian Ocean archipelago.
However, an investigation by the Comoros parliament released earlier this year found that thousands of passports were sold outside official channels via “mafia” networks and at least 100 million dollars of revenues went missing.
A court document, dated Aug. 20 and seen by Reuters, showed Sambi also faces charges linked to forgery and falsification of records.
Neither the document nor the prosecutor gave details on when any trial might take place.
Mahamoud Ahamada, one of Sambi’s lawyers, confirmed that Sambi had been charged and restrictions on him had been tightened, even though he was still sleeping in his own home.
“Sambi no longer has access to his telephone and the conditions of his detention are prison-like,” he said.
“It seems he has been detained and charged in relation to the (passport) issue.”
Sambi’s lawyers had challenged his house arrest and argued that the move was an attack on democracy in Comoros.
Current President Azali Assoumani has just won a referendum that will extend presidential term limits and end the system of rotating power between the archipelago’s three main islands.
Reuters/NAN